As related to the principles of operant conditioning, a stimulus must be present for an operant response to be reinforced.

answer; for children with two myopic parents,the likelihood of becoming myopic is ) correlated with the number of hours spent playing sports each week;

mali had been a state inside of the ghanaian empire. after ghana fell because of invading forces and internal disputes, mali rose to greatness under the leadership of a legendary king named sundiata, the "lion king." the songhai empire, already weakened by internal political struggles, went into decline.

i need more info !